The United Nations health agency has confirmed a fatal human case of bird flu in Nigeria, Africa?s most populous country, only the second incidence of the H5N1 virus in humans in the sub-Saharan region, and is working with the Nigerian authorities to identify the source of infection.

All samples from contacts of the victim, a 22-year-old woman from Lagos, Nigeria?s largest city, have so far tested negative, the UN World Health Organization (WHO) said. The women?s infection with the H5N1 virus was confirmed by the WHO Collaborating Centre for Reference and Research on Influenza in London.

The agency noted that H5N1 has been identified in poultry outbreaks in Nigeria and, as in other affected countries, sporadic cases of human infection are not unexpected. The only other sub-Saharan African country to report human bird flu is Djibouti with one non-fatal case. North of the Sahara only Egypt has had human cases ? 19 with 11 of them fatal.

There have so far been 271 confirmed cases worldwide, 165 of them fatal, the vast majority in South-East Asia. Ever since the first human case of H5N1, linked to widespread poultry outbreaks in Viet Nam and Thailand, was reported in January 2004, UN health officials have warned that the virus could evolve into a human pandemic if it mutates into a form which could transmit easily between people.

The so-called Spanish flu pandemic of 1918-1920 is estimated to have killed from 20 million to 40 million people worldwide. More than 200 million birds have died worldwide from either the virus or preventive culling.

There is one other suspected death from the virus in Nigeria and WHO is working with the Government to carry out intensive surveillance. Reports of additional suspected cases may occur as people with influenza-like symptoms seek medical advice.

Meanwhile UN System Coordinator for Avian and Human Influenza David Nabarro said the chances of human infection from an outbreak among birds in the United Kingdom were very small, but the world needs to remain vigilant for up to a decade to ensure the virus?s eradication.

WHO stressed that H5N1 is not transmitted to humans through properly prepared and cooked food. Cases of human infection have frequently been linked to the home slaughter and subsequent handling of diseased or dead birds prior to cooking and these practices represent the highest risk of human infection.

When handling raw poultry or live or dead birds, it is imperative to disinfect hands and surfaces with soap and water, WHO said. Consumers also need to be sure that during the cooking process, poultry reaches temperatures of at least 70 centigrade in all parts and that eggs are fully cooked throughout.